The following discussion addresses automotive applications, as this is the field in which significant improvements in efficiency may be realized by the described invention. The average automobile engine only achieves its maximum power rating when accelerating at the maximum obtainable rate, traveling uphill at a high rate of speed or traveling at maximum obtainable speed. Since most vehicle operation requires only a fractional portion of available engine power part throttle efficiency becomes a major factor in the fuel economy experienced by the average automobile. Part throttle efficiency is not as significant for vehicles with a low power to weight ratio such as medium and large trucks or severely underpowered smaller vehicles. Increasing part throttle efficiency has recently become a more desirable goal for automobile producers with production of higher-powered vehicles trending upwards and the possibility of increases in legislated fuel mileage standards.
Heating of combustion air for spark ignition engines has been employed in the past in a limited manner. Combustion air has been heated by contact with a shrouded exhaust manifold and supplied to the engine by admittance to the engine air filter as controlled by a thermostat. The purpose of this arrangement was to provide heated air during cold engine and cold ambient conditions to aid in fuel vaporization and provide air at temperatures closer to that of those experienced at normal operation. Also carburetor-icing phenomenon were less likely to occur with this system. Additionally intake manifold heating by either exhaust gases or engine coolant have been used with the primary purpose of aiding fuel vaporization. Combustion air heating also occurs as a result of intake manifold heating. These methods were used with carbureted engines, which did not have provisions for maintaining the optimum fuel air ratios when intake air density changed due to changes in temperature or atmospheric pressure.
The disadvantage to combustion air heating is that the density of the incoming air will be reduced with a resultant reduction in the maximum available power. For this reason current automotive practice is to obtain combustion air in front of the vehicles radiator, which provides the coolest, air obtainable. Adequate fuel vaporization is obtained with the cooler air by injecting the fuel at each intake port relying on the fuel injector and heat transfer from the cylinder head as well as heat introduced by exhaust gas re-circulation.
This invention provides a method of improving efficiency by controlling combustion air temperatures based on power demand to achieve maximum efficiency. Control is by integrating combustion air temperature control with the other engine management functions. Existing patents are discussed below as to their purpose and relevance to this invention. Since this invention does not deal with the specific details of the devices required the following discussion is based on the objectives of the previous inventions.
Patents that provide heated combustion air for engine starting and subsequent warm up are not listed or discussed, as their primary objectives are significantly different than that of this invention.
Patents that apply to methods for heating combustion air to preclude icing or condensation phenomena are not listed or discussed for the same reason. Additionally patents that provide an electrically controlled manifold xe2x80x9chot spotxe2x80x9d are not discussed as they are considered a refinement of the manifold heating processes discussed above.
Numerous patents have been issued which deal with the process of providing heated air to the engine at a relatively constant temperature as discussed above. Some of these inventions also provide a means of providing cooler ambient air when the cool air is desirable for maximum power output. These inventions were thermostatically controlled by a mechanical or electrical means to provide an optimum temperature for a predetermined engine temperature and predetermined fuel addition capability. These patents are considered improvements or variations of the combustion air heating method described above and include U.S. Pat. No. 4,249,500 (Behrendt) and others listed in the Cross Reference to Related Patents Listing that are not specifically addressed below.
U.S. Pat. No. 4,545,357(Kearsly) describes a programmable temperature control system for combustion air. That patent provides temperature control but does not provide for integration with fuel delivery and other control parameters that require adjustment as combustion air temperatures are widely varied.
U.S. Pat. No. 4,723,527(Panten) utilizes controlled combustion air temperatures. It comprises a 2-stage control system coupled with controlled EGR valve operation.
U.S. Pat. Nos. 5,076,248(Schutz), 5,404,844(Schechter) and 5,996,560(Schechter) contain provisions for providing heated combustion air during part throttle operation. The heated air is provided primarily as an aid in maintaining stable combustion when variable valve timing changes are implemented in these applications.
Spark ignition engines suffer a loss of efficiency during part throttle operation due to pumping losses created by the high vacuum conditions existing in the engine cylinder during the intake stroke. Some of this loss may be eliminated by heating the combustion air to a high temperature. Since a higher volume of the hotter less dense air is required to produce the same power output a larger throttle opening with a resultant lower manifold vacuum would result in a reduction of pumping losses. Efficiency gains would also be achieved by recycling waste heat thru the compression/combustion expansion process resulting in an increase in thermal efficiency. Heating the combustion air can also result in improved fuel vaporization and combustion stability.
The advantages would be achieved by heating ambient air to a high temperature utilizing engine produced waste heat and mixing the hot air with ambient air to create a controlled temperature combustion air supply. The amount of ambient air mixed with the heated air would vary from little or none at low throttle demand to 100% ambient at full throttle demand. The high temperature combustion air system would be controlled by the fuel management computer programmed to provide the hottest possible combustion air temperature based on power demand, engine pre-ignition or detonation limits and pollution (primarily nitrogen compounds) limits.
The additional components necessary to achieve the objectives would consist of heat exchanger(s), a mixing valve with operator, additional temperature sensors and necessary ducting. Current fuel management controls would require extended capabilities to manage combustion air temperature as well as manage fuel delivery over the extended range of combustion air density.
Additionally a throttle by wire feature and hot air dump valve with a circulation fan are desirable. The throttle by wire feature is currently used in some automotive applications and is desirable to prevent exceeding system response rates and to maintain engine power in accordance with operator demand during transit conditions. A hot air dump valve located downstream of the combustion air heat exchangers is desirable to maintain the hot air supply at a relatively constant temperature. A fan to maintain air circulation thru the heat exchanger when induced airflow (by vehicle movement) is not sufficient is required to ensure air temperature control is maintained. The fan may be the normal radiator cooling fan or a separate fan. Control of the dump valve and fan would be by the engine management system or directly by thermostatic controls.